1. Field of the Invention
The present invention relates to collation device, registration device, image correcting method and program, and is suitable for use in an authentication device based on a biometrics authentication.
2. Description of the Related Art
In related art, a blood vessel is one of subjects to biometrics authentication. In general, in an authentication device, a finger, for example, is fixed on an image pickup camera in parallel with the imaging surface thereof to image the blood vessel of the finger to be fixed. The image of the blood vessel obtained as a result of imaging is registered in a memory as information for authenticating the human body imaged at that moment or compared with the registered image of the blood vessel to determine whether to authenticate the registrant or not.
It is inconvenient for a user to fix his or her finger on the image pickup camera in imaging a blood vessel. From a user-friendly point of view, there is a request to position a finger on an image pickup camera without constraint.
When the blood vessel of a finger freely positioned on the image pickup camera is imaged, it is most presumable that a difference can be made in a state where the finger is positioned on the image pickup camera at the times of registration and authentication.
Actually, one of typical differences between states where the finger is positioned at the times of registration and authentication includes an angle made by the imaging surface of the image pickup camera and the finger positioned above the image pickup camera, that is, a tilt of the finger with respect to the imaging surface.
When the finger is imaged while tilted relative to the imaging surface, the finger in an blood-vessel image obtained as a result of imaging is distorted because the contour of the finger corresponding in position to a part nearer to the image pickup camera is longer and that of the finger corresponding in position to a part farther from the image pickup camera is shorter.
In an authentication device, if the distortion of the finger in the image (projection distortion) is caused between the times of registration and authentication, this may cause an inconvenience that the authentication device takes a registrant himself/herself for another person and vice versa. This results in degradation in an authentication accuracy.
As one of methods of removing such projection distortion, the following patent literature discloses a method in which an image is corrected in such a manner that any one of lengths of the contours corresponding in position to a part nearer to the image pickup camera or to a part farther from the image pickup camera is matched to the other (for example, refer to Jpn. Pat. Appln. Laid-Open Publication No. 2000-22869 (FIGS. 11 and 12)